Glass melting has traditionally been accomplished in open-hearth type furnaces. In these traditional furnaces, pulverulent raw batch materials are distributed on top of a molten pool of glass to form a batch blanket. In gas fired furnaces, radiation from the furnace crown and combustion flames supply the energy required for heating and melting the batch materials. Although over the years numerous design and operating changes have been incorporated into these furnaces, there are still many deficiencies associated with these tank type glass furnaces. In modern tank type furnaces, the multiple subprocesses of continuous glass melting are expected to accomplished in a single pool of glass of which the physical dimensions are maintained constant. These subprocesses include distribution of raw batch materials to form a batch blanket and control of its movement, heating and melting the batch materials, dissolving silica grains, homogenizing the glass, and refining the glass to allow gaseous inclusions to be released from the melt. All these subprocesses have to be accomplished within a minimum glass residence time inside the furnace. However, the mechanisms involved in each of the subprocesses are not necessarily the most efficient, and some are not even compatible with each other. In order to produce an acceptable glass, the solution to the aforementioned deficiencies relies on having a large body of glass in the tank to provide sufficient time for the subprocesses to complete before the glass is delivered to the forming operations. This is a very costly way to produce glass because the construction and maintenance of the furnaces require an excessive amount of expensive materials, huge superstructures, and numerous labor-intensive auxiliary items which lead to high furnace capital, operating, and maintenance costs. Further, although the furnaces are extensively insulated, a significant amount of energy input is needed to maintain the pool of glass at desired temperatures due to furnace heat losses which results in high furnace operating costs.
Many attempts have been made throughout the history of glass making to overcome the deficiencies associated with open-hearth tank type furnaces. U.S. Pat. No. 4,553,997, issued to Hnat, and U.S. Pat. No. 3,748,113, issued to Ito, each teach a glass melting apparatus where glass batch materials and either heated combustion products or a fuel-air mixture are injected together into the interior of a melting chamber to form a swirling flow pattern for the production of molten glass. However, in each of these devices the effectiveness of the swirling flow, or vortex, on the batch heating and melting processes, is necessarily weakened by the inclusion of the batch materials in the vortex-forming flow of injected materials. Since the batch materials are injected with either the combustion products or the fuel-air mixture, the high shear forces in the vortex for enhanced energy and mass transfer, are not effectively utilized to promote batch heating and melting. U.S. Pat. No. 2,268,546, issued to Forter, describes a glass furnace wherein fuel and air for combustion are introduced into the furnace to form burning streams of fuel in the form of a vortex. Batch materials are introduced downstream of the vortex, as opposed to within the vortex. In this manner, the heated vortex is utilized to uniformly heat the batch blanket of a pool of molten glass moving beneath the vortex. This device does not take advantage of the turbulence of the vortex to heat the batch materials as they are introduced into the furnace. Rather, the vortex is merely used to uniformly heat the batch blanket of the pool of molten glass.
U.S. Pat. No. 4,957,527, issued to Hnat, describes an apparatus for heat processing batch materials wherein preheated air is utilized to create a well-stirred vortex flow pattern within the furnace. Fuel and batch materials are introduced into the furnace along the centerline of the preheater so as to pass through the vortex. Fuel is generated in a gasifier prior to being injected into the preheater. However, it is difficult to maintain efficient and adequate batch melting within the furnace because the temperature of the vortex is not elevated until the fuel reacts with the oxidant within the vortex. Further, the well-stirred flow pattern in the preheater does not have the mechanism to separate the heated batch from the products of combustion. As a consequence, the glass produced downstream of the preheater is expected to contain large amounts of seeds. For these reasons, the furnace described in U.S. Pat. No. 4,957,527 is used primarily for waste materials processing as opposed to glass melting operations.
U.S. Pat. No. 2,455,907, issued to Slayter, describes an apparatus for melting glass wherein gas burners are directed so as to create a swirling or cyclonic flame in a melting chamber. According to the Slayter patent, as the glass batch is discharged into the chamber, the finely divided particles are immediately impinged by the swirling flame and reduced to a molten state. However, the design of the Slayter patent is not conducive to glass production because the products of combustion exit the chamber with the molten glass, thereby entraining gas within the molten glass. Further, as the molten glass exits the melting chamber, it is deposited into a pool of molten glass, thereby creating surface discontinuities within the pool of molten glass and causing further gaseous inclusions within the molten glass.
Finally, regarding the teachings of the patent documents described above, each of the devices described therein utilize a vertically oriented batch melting chamber. The heated batch materials or molten glass that were separated from the products of combustion in these melting chambers (except U.S. Pat. Nos. 4,957,527 and 4,533,997 wherein all the materials are in a mixed state), are remixed with the products of combustion at the chamber exit. As a result, the glasses produced from these melting chambers tend to be foamy or seedy. The vertical orientation of the melting chamber is also problematic because of structural incompatibility with many glass production and refining assemblies, which are commonly oriented along a horizontal plane.
Accordingly, there is a need for an improved apparatus for melting batch materials wherein efficient and complete batch melting is accomplished, wherein the integrity of the molten glass is preserved, and which is compatible with existing production assemblies.